Engineering Papers⌕ Search

Engineering topics

Winningham, J. D.

Publications and source records attributed to Winningham, J. D..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Numerical model of the convecting F2 ionosphere at high latitudes

In previous work Knudsen (1974) presented a model for the convection field of the high latitude F layer and evaluated the time-dependent behavior of a tube of F layer plasma carried around the polar regions by the field. The present paper describes the initial results of a more detailed numerical study of the behavior of the F layer tubes, where it is assumed that the tubes are subjected to time-dependent ionization rates from both solar photons and precipitating energetic electrons. The numerical results are presented in the form of a map view of N-m F2 contours, electron concentration in vertical section over the magnetic pole from noon to midnight, and several vertical profiles of electron concentration for both convecting and nonconvecting flux tubes. The proposed convection field produced a tongue of F layer plasma extending from the dayside of the cleft over the polar cap with concentrations consistent with those observed by Isis 2.

Knudsen, W. C.↗
NASA NTRS1977

Rocket-borne measurements of the dayside cleft plasma - The Tordo experiments

Results are presented from low-energy plasma analyzers (12 eV to 12 keV) carried on two rockets launched into the dayside cleft during January 1975. It is concluded that (1) atmospheric interaction becomes important for less than 1-keV electrons at approximately 250 km, (2) characteristics of particles in 'inverted V's' observed in the afternoon cleft are consistent with their interpretation as being due to parallel electric field acceleration from a constant source population, and (3) magnetospheric energetic (greater than 2 keV) electrons intermingle with magnetosheathlike plasma in the cleft.

Winningham, J. D.↗
NASA NTRS1977

Ionosonde observations of the northern magnetospheric cleft during December 1974 and January 1975

During December 1974 and January 1975, the northern magnetospheric cleft was monitored by ionosondes at Cape Parry and Sachs Harbor, Northwest Territories, Canada, in support of rocket shots into the cleft. Ionograms were taken nominally at 15-min intervals but as rapidly as two per minute during times of particular interest. Analysis of 5 days of data shows the ionosphere at cleft latitudes to be very complex and dynamic. The ionograms often show considerable structure and can change appearance significantly in a minute or two. The cleft at times appears to move equatorward in response either to a southward turning of the interplanetary magnetic field or to the occurrence of geomagnetic disturbances. This response is in agreement with the conclusions of previous satellite studies. Behavior contrary to this generalization is not uncommon, however, and therefore it may not always hold on time scales considerably shorter than the satellite orbital period of at least 1 hour. The rate of the cleft's motion may vary from about 0.05 to 0.5 deg/min.

Stiles, G. S.↗
NASA NTRS1976

Dependence of the latitude of the cleft on the interplanetary magnetic field and substorm activity

The latitudinal motion of the cleft (the polar cusp) associated with the southward interplanetary magnetic field (IMF) and substorm activity is examined. The cleft location is identified on the basis of the location of midday auroras and of electron precipitation by the OGO 4 and ISIS 1 satellites. It is found that the IMF and substorm activity control independently the latitude of the cleft and that they can shift the cleft location by 3 or 4 deg under average conditions.

Kamide, Y.↗
NASA NTRS1976

A snapshot of the polar ionosphere

This paper presents a picture of the north polar F layer and topside ionosphere obtained primarily from three satellites (Alouette 2, ISIS 1, ISIS 2) that passed over the region within a time interval of about 50 min on a magnetically quiet day. The horizontal distribution of electron densities at the peak of the F layer is found to be similar to synoptic results from the IGY. Energetic-particle and ionospheric-plasma data are also presented, and the F-layer data are discussed in terms of these measurements as well as in terms of electric-field and neutral N2 density measurements made by other satellites on other occasions. The major feature observed is a tongue of F-region ionization extending from the dayside across the polar cap, which is accounted for by antisunward drift due to magnetospheric convection. In the F layer and topside ionosphere, the main effect of auroral precipitation appears to be heating and expansion of the topside. A region of low F-layer density appears on the morning side of the polar cap, which may be due to convection and possibly also to enhanced N2 densities.

Whitteker, J. H.↗
NASA NTRS1975

Rocket-borne particle, field, and plasma observations in the cleft region

Results are reported for comprehensive observations of magnetic and electric fields together with ambient and suprathermal plasmas above the dayside auroral oval with rocket-borne instrumentation which penetrated the cleft region. Measurements were also obtained equatorward and poleward of the cleft. Convection velocities as inferred from electric-field measurements were generally toward noon equatorward of the cleft and were antisunward over the polar cap. Observations of electron temperatures, electric fields, and low-frequency electrostatic noise provide strong evidence of a plasma instability (Farley-Buneman) in the E-layer associated with the appearance of the 'slant E condition' identified in ground-acquired ionograms. The positions of these measurements relative to that of the cleft were firmly established via the determination of the plasma environment with an electrostatic analyzer.

Ungstrup, E.↗
NASA NTRS1975

The latitudinal morphology of 10-eV to 10-keV electron fluxes during magnetically quiet and disturbed times in the 2100-0300 MLT sector

Electron and proton data from Isis 1 and 2 have been used to examine the change in the latitudinal morphology of auroral particle fluxes as a function of substorm time in the dipole magnetic local time period from 2100 to 0300. Clear and repeatable systematics in the latitudinal morphology were observed during the various phases of a substorm, allowing the substorm phase to be identified on the basis of particle data alone. Based on this study, a new phenomenological substorm model is presented which relates particle precipitation from various parts of the magnetotail to auroral oval morphology.

Winningham, J. D.↗
NASA NTRS1975

Two barium plasma injections into the northern magnetospheric cleft

Two rocket experiments, performed in January 1975, investigated convection of plasma formed by solar photoionization of barium injected into the northern magnetospheric cleft at 13 km/s upward and parallel to the local geomagnetic field. Plasma convection was demonstrated from the cleft's poleward region, directly into and across the polar cap, and possibly into the convection system of the nightside auroral electrojet; plasma injected centrally within the cleft under quiet magnetic conditions remained in the cleft convection system for at least 22 min and revealed a highly structured E-field over about 600 km of longitudinal extent. Cleft location agreed with that predicted by ionosondes.

Jeffries, R. A.↗
NASA NTRS1974

Low energy (10eV to 10 keV) equatorial particle fluxes and soft particle fluxes near the equator

Several spectra are shown that represent one rotation of ISIS-1. Spectra 1, 2, 3, represent particles moving down the field line into northern ionosphere and spectra 4, 5, 6 represent particles moving up field lines towards the magnetic equator. The former are direct fluxes and the latter are albedo fluxes. The spectra observed are remarkably similar to these observed in the auroral zone. The direct fluxes exhibit a relative maximum in the few keV range and the albedo a power low spectrum with increased fluxes at low energies. Examination of concurrent topside sounder data on ISIS-1 revealed a positive correlation between a region of turbulent ionosphere and particle fluxes. This ionospheric condition is referred to as equatorial spread F and has been studied extensively with bottomside ionospheric sounders and backscatter radars. The perigee of ISIS crossed the magnetic equator at four local times (0400, 1000, 1600, 2100) during the lifetime of the particle spectrometer. No fluxes were observed at 0400 and 1000 local time. At 1600 a few instances of particles were observed. At 2100 essentially all passes included detectable equatorial fluxes. This is in agreement with the frequency of occurence of equatorial spread F.

Winningham, J. D.↗
NASA NTRS1974

Polar cap auroral electron fluxes observed with Isis 1

Three types of auroral particle precipitation have been observed over the polar caps, well inside the auroral oval, by means of the soft particle spectrometer on the Isis 1 satellite. The first type is a uniform, very soft (about 100 eV) electron 'polar rain' over the entire polar cap; this may well be present with very weak intensity at all times, but it is markedly enhanced during worldwide geomagnetic storms. A second type of precipitation is a structured flux of electrons with energies near 1 keV, suggestive of localized 'polar showers'; it seems likely that these are the cause of the sun-aligned auroral arcs that have been observed during moderately quiet conditions. During periods of intense magnetic disturbance this precipitation can become very intense and exhibit a characteristic pattern that we have come to call a 'polar squall'.

Winningham, J. D.↗
NASA NTRS1973

The effect of conjugate photoelectron impact ionization on the pre-dawn ionosphere

The measured photoelectron fluxes are used to show that ionization by photoelectrons is not sufficiently large to affect significantly the nighttime ionosphere. The measured downward photoelectron flux used in the calculations is shown in a table. This flux was measured on December 9, 1971 at an altitude of 1400 km, when the local zenith angle was 159 deg and the conjugate zenith angle was 85.2 deg.

Nagy, A. F.↗
NASA NTRS1973

Equatorward shift of the cleft during magnetospheric substorms as observed by Isis 1

Isis 1 satellite observations of the cleft position during magnetospheric substorms show that the cleft shifts equatorward as the interplanetary B sub z component turns southward and substorm activity increases and that it shifts back toward higher latitudes as substorm activity subsides and B sub z returns northward. Also, unusually low latitudes for the cleft (less than 70 deg invariant latitude) were found during geomagnetic storms with significant Dst values and large negative B sub z values. Significant shifts occur in the cleft location with no accompanying effect seen in the AE index; however, B sub z is observed to be southward during these periods.

Yasuhara, F.↗
NASA NTRS1973

Simultaneous observations of auroras from the South Pole Station and of precipitating electrons by Isis 1.

On the basis of the simultaneous observations of auroras from the South Pole and of precipitating electrons by the Isis 1 satellite it is shown that (1) a midday auroral arc (photographed on black and white film) occurs within the cleft (cusp) region projected to the appropriate auroral height along the geomagnetic field; (2) in the evening sector an aurora, observed by Isis 1 and the South Pole all-sky camera, extended for at least 5 hours of local geomagnetic time in the expected position of the auroral oval; and (3) during a period of extreme magnetic quiet, cleftlike electrons were observed just poleward of a narrow region of intense precipitation in the midnight sector. An earth-sun oriented arc was seen at the projected location of the intense electron flux.

Winningham, J. D.↗
NASA NTRS1972

Auroral emissions and particle precipitation in the noon sector.

Comparison of airborne optical measurements during December 1969 with satellite particle measurements made earlier in 1969. The latitudinal distributions of H beta, 4278-A and 6300-A emissions during quiet periods are observed to agree with what would be expected from the latitudinal distribution of particle precipitation during similar conditions. In particular, there is a belt 200 to 500 km wide (at ionospheric heights) in which the magnetosheath plasma penetrates down to low altitudes through the cusps in the dayside magnetosphere and in which both H beta and 6300-A emissions are observed. There are brighter red arcs with green lower borders within this belt. It is suggested that these are produced by narrow regions of precipitation of slightly more energetic electrons embedded in the cusp fluxes. Poleward of this belt the flux of particles is low, and the atmospheric emissions are very weak, except for occasional narrow regions of electron precipitation (without measurable protons) and the corresponding polar-cap aurora (without the H beta emission).

Heikkila, W. J.↗